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Speed Vest 

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Speed Vest 

Written By: Mykle Hansen 


Computer (1) 

EL wire stripper (1) 

if you cut your own EL wire 

Lighter (1) 

Multimeter (1) 

Needle Nose Pliers (1) 

Plastic sheet (1) 

Print Gocco screen printing kit (1) 
available on eBay 

Scissors (1) 

Soldering station (1) 

USB cabled) 

X-Acto knifed) 



We chose the Mil Spec Mesh Vest $55 
from Icon (, a high- 
visibility motorcycling vest with a handy 
rear pocket to hold the electronics. 


Arduino ProtoShield kit (1) 
$16 from the Maker Shed 
(http.V/makershed. com) 

Arduino USB microcontroller (1) 
$35 from SparkFun Electronics 
( or the Maker Shed 

Buttoneer (1) 

or a needle with monofilament thread. 
The Buttoneer is $12 from fabrics or 
sewing supply stores. 

Denim (1) 


to house the control circuit and wires. 

Triacs (8) 

Digi-Kev part #MAC97A6QS-ND. 

© Make Projects 

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Speed Vest 

http.V/digikey. com 

Heat-shrink tubing (1) 

resistors (12) 

resistors (1) 

safety pins (1) 

Wheel sensor (1) 

The sensor must perform like a reed 
switch, which is binary, rather than use 
the magnet on the spoke to vary the 
inductance. We used a Sigma Sport BC 
500. which costs $15, but the city of 
Portland gives them to residents free, to 
encourage bicycling! Ask a bike shop if 
they can sell you just the wheel sensor 
part, without the computer and display. 

Batteries (1) 

Batteries (1) 

Male header (1) 

Ribbon cable (1) 

EL wire (1) 

$20 from Coo Light ( 

You'll need 12 segments of wire. 16" 
long with 10" leads. If you don't want to 
cut and solder your own, the folks at 
CooLight can do it for $2.50 per 
segment. Also available at Light 'n Wire 
productions ( 

Foil tape (1) 

if you cut your own EL wire 

EL wire power supply (1) 

We used CooLight part #CL-IPSF3, $6, 

which takes 1 AA battery and can light 

EL wire segments up to 16" long. 

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Speed Vest 

Reflective tape (1) 

\Ne used 3M Scotchlite Iron- On from Or use sew-on 
reflective letters from 
http.V/searchgear. com. 

Electrical Tape (1) 


This lightweight night-cycling vest displays your current speed in glowing, 7-inch-tall 
numbers easily visible to cars. On the back, an Arduino microcontroller reads input from an 
off-the-shelf bike speedometer sensor, and then switches power to sewn-in numerals made 
from electroluminescent (EL) wire. 

Bicyclists receive a lot of honk-based grief from car drivers who perceive them as slow and 
in the way, and when drivers misjudge a bicycle's speed, it can cause "right hook" collisions 
that kill several bicyclists each year. If car users knew how fast cyclists were moving, would 
they be more willing to share the road? What if a bicycle prominently displayed its speed to 
the cars behind it, using large, brightly lit digits? 

Brady Clark, cycling advocate and design genius, asked me to help him answer this 
question. At first I assumed it was beyond me, since I was a software guy who barely 
understood electronics. But I love to learn, and the Dorkbot community in Portland, Ore., 
was encouraging and helpful. 

Our final motivation was the Bike Gadget Contest in Minneapolis, sponsored by the Bell 
Museum and The Hub, a bike co-op. After some research and shopping, we completed this 
project in a manic three-day push, then delivered it to the contest judges within minutes of 
the entry deadline. 

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Speed Vest 

• The ProtoShield lets you build 
circuits directly on top of the 
Arduino board. I assembled it 
following Atomicsalad's excellent 
ProtoShield tutorial . 

• If you're really in a hurry, you can 
leave out all the female headers. 
But if you might use your 
ProtoShield for other projects later 
it's better to assemble the whole 
thing (and you'll still have to do a 
lot of desoldering.) 

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Speed Vest 

• For each display digit, an Arduino output pin connects through 1 resistor to 1 triac. The 
other 2 pins of the triac connect to ground and the digit's ribbon cable pin. It's a simple 
circuit; the tricky part is fitting 12 of them onto the ProtoShield. (There are too many 
connections to use the ProtoShield's mini solderless breadboard.) Here's how I did it. 
Refer to the schematic for all connections. 

• Plug the 2x7 male header across the middle of the board, perpendicular to the rails and 
with one end adjacent to the ground (GND) rail. 

• Plug in the 100Q resistors just below the 5V rail in 2 rows of 6, grouped on either side of 
the male header. Underneath, connect one end of each to one of the D0-D13 contacts, on 
the female headers if present, or else on the board itself. Leave D3 empty for the speedo 
interrupt. To save room, orient the resistors vertically. 

• Arrange triacs at the intersection of each resistor and header pin. For each triac, the gate 
lead (pin 2, the middle pin) will connect through a resistor to one of the Arduino's digital 
outputs D0-D13. This pin controls the flow between the other 2, like the base of a 
transistor. Pin 1 of the triac, on the left as you read the printing on its face, connects to 
ground, and pin 3 connects to the ribbon cable via the 2x7 male header. 

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Speed Vest 

• On the underside of the board, connect the resistors, triacs, and ribbon cable header 
following the schematic. I simply bent and soldered down the uncut leads, rather than the 
usual method of trimming leads and connecting with insulated wire. Apologies to any 
professional electrical engineers who are nauseated by this. 

• Connect the speedometer sensor's 2 wires to power (5V) and one of the Arduino's interrupt 
pins, D2 or D3 (I used D3). Also tie that same pin to ground with the 1kQ resistor; 
otherwise, your sensor might detect nonexistent ghost bikes in your vicinity. Different 
ProtoShields have different layouts, so you should make these connections wherever it 
makes sense for your board. 

• On the one shown here, made by MAKE intern Kris Magri, the speedo connects to one end 
of the 5V rail and an adjacent hole, which is wired up to D3 on the underside. The 1kQ 
resistor fits into the row of 100Q resistors and connects to ground. 

• On my v.1 ProtoShield, the power, ground, and D3 pins all sit on the BlueSMiRF header, 
so I plugged the speedo in there. This project doesn't use Bluetooth, and the BlueSMiRF 
header was a handy place to connect. 

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Speed Vest 

• Connect the EL wire power 
supply's black wire to the board's 
ground rail and its red wire to both 
adjacent pins at the end of the 
ribbon header, bridging the 3 pads 
underneath. This divides the power 
so that one ribbon wire feeds the 
left digit and the other feeds the 

• Use electrical tape to insulate all 
exposed conductors, and shrink 
any heat-shrink tubing you've 

• Solder one lead from each digit 
(either lead) to individual wires of 
the ribbon cable. These are the 
grounds. You can be systematic 
and plan ahead which pin goes to 
which numeral, but we decided not 
to keep track and to make the 
associations later in the software. 

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Speed Vest 

• Download and install the latest Arduino software from . On older versions 
of Mac OS X, you may also need to install the provided USB Serial Driver, so that your 
computer sees the Arduino as a serial port. 

• With the ProtoShield unplugged, hook the Arduino to your computer. Download and run the 
"Blink" example code, on the Arduino site under "Learning/Examples," to prove that your 
whole toolchain works. 

• Download the test software Test EL Digits .pde . Plug the ProtoShield into the Arduino and 
the ribbon cable into the ProtoShield. 

• Run the test software, which cycles through each output pin in order, so you can spot any 
bad connections. Quality control and breakage can be an issue with EL wire, so handle it 
gently and make sure each segment works. One bad segment can short out the whole 
circuit, in which case you should check the resistance across all of them. 

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Speed Vest 

• If you're working with plain EL wire rather than prepared segments, you need to connect 
leads to the core and wrap wires of each piece. Cut the EL wire into 16" segments, and 
burn off 1" of the outer sleeve at one end to expose the wrap wires. Make 12 of these 

• To make a solderable contact for the wrap wires, you can carefully tease them to one side 
and twist them together, or else belt them with a snug loop of copper tape. Then use a 
knife or stripper to remove the phosphor underneath and expose the core wire. 

• Split and strip a dozen 10" leads, then solder the EL core and wrap wires to separate lead 
wires. Use heat-shrink tubing to insulate and reinforce the joints, remembering to slip the 
pieces over the leads before soldering. 

• Download the digit template stacked numbers template.pdf , print it, and pin it to the V 
square of thick black cloth. 

• Pin the cloth around a frame of plastic or cardboard, then run strands of EL wire along the 
path of each digit, entering and exiting through holes cut in the backing cloth at the bottom 
of each numeral. 

• To anchor the EL wire to the fabric, we used a great tool the CooLight folks hipped us to: 
the Buttoneer. It's designed to attach buttons to clothes using small plastic staples, but it 
also works brilliantly for attaching EL wire. 

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Speed Vest 

• EL wire can't take sharp bends without breaking. To create the hard corners that 
discerning digit-users crave, run it out the back through a hole, loop it around underneath, 
and bring it back up at the different angle. 

• Once the digits are affixed, rip away the paper underneath, bit by bit. 

• Trim any excess EL wire off the digits. If you're using precut segments, move the end 
caps onto the new ends; otherwise, cap the ends with a bit of heat-shrink. 

• For the other, non-ground leads, twist them together into a single mass on each side of the 
ribbon cable and solder them to the 2 pins that connect to the power supply. 

Download and run the Speed Vest software, speedo 4.pde , as in Step 5. When the 
program starts, it cycles through each output pin in order, so you can identify which pin 
feeds to which digit. At this point the numbers should light up in random order. 

Unplug the ProtoShield and use a multimeter to probe and map the connections between 
the Arduino output pins and the digits. Then edit the array definitions for onesPins and 
tensPins at the top of speedo_4.pde\o reflect the associations. Edit and rerun the software 
as needed until the numbers boot up in order. 

Test the system on the bench by holding the 2 halves of the wheel sensor and brushing the 
magnet past the switch in a regular rhythm, to simulate the rotation of a wheel. At this 
point, we found it very gratifying to see our work light up! 

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Speed Vest 

• Now attach the hardware to the 
vest. We used velcro tape, but with 
hindsight I recommend you sew it 
or use plain old safety pins. 
They're cheaper and more secure, 
and we haven't yet needed to 
remove and reconnect the display. 

• (Optional) Brady used his beloved 
Print Gocco miniature screen- 
printing kit to add some extra 
safety-bling to the vest: a reflective 
"MY SPEED" banner to run along 
the top. You could also just use 
reflective paint or tape. 

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Speed Vest 

Step 10 — Oops! Quick— build a case! (duh!) 

It's stunningly un-chic to have dangly bits of electronics trailing out behind your butt, or 
tangled in your spokes. But somehow, we failed to foresee the obvious need for a case. 
Under extreme deadline pressure, our original Speed Vest had a ghetto-tech case made 
from scrap cardboard and rubber bands. 

For the version shown here, built by Kris from MAKE, she used a plastic soap dish, and 
then after that disappeared from the lab, she tucked it into a small box. The case just fits 
into the pocket of the vest, so it isn't visible, but I'll still bet you can do better! 

We ran the ribbon cable through a tiny slit in the integrated rear pouch of our vest. The 
case fits snugly in the pouch, hiding all our sloppiness while letting our invention shine! 

Special thanks to Nick Sanders at West County Cycle Service for his help with our build. 

The Display Mannequin 

With less than 12 hours remaining before our all-motivating contest deadline, we began work on 
our floor display. We made a mannequin to wear the Speed Vest by casting Brady, using Mark 
Jenkins' packing tape sculpture technique ( ). Add one bicycle and one 
bicycle work-stand, and we were ready to wow the public. 

SpeedVest II 

It's hard to know just how car drivers feel about the Speed Vest, but so far nobody bicycling 
while wearing it has been honked at or run over. Meanwhile, we're now working on SpeedVest II, 
with four major areas of improvement: 

Wirelessness If the rider forgets he's plugged into the bicycle when he dismounts, the electronics get yanked. In practice, 
this happens almost every time, and we've had to resolder the connectors three times already. SpeedVest II will use Zigbee 
wireless modules to transmit speed data from the wheel to the Arduino.Size In bicycle equipment, lightness is everything. 
The Arduino USB board is handy, but contains a lot of parts we don't use. With a custom PCB design, we can get the whole 
system much smaller and lighter. Power The Arduino is powered by a 9V battery, but the EL wire inverter has its own AA 

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Speed Vest 

battery and a separate power switch. The batteries run out at different times, and turning the unit on and off is a two-step 
process. Our improved single-board design will integrate the inverter, driven from the same power source as the rest of the 
board. Speed range Bicycles are fast, and getting faster! Our vest displays speeds up to 69mph, but the current bicycle land 
speed record is 81mph. (And that's not even close to the drafting speed record of 152mph, set by a bicyclist chasing a 
specially designed car that pushed away the forward wind resistance.) So we're redesigning our numeric display to show all 
speeds from 1 to 99 miles per hour. We hope that will suffice for normal use. 

The Contest 

We handily accomplished our first mission: winning The Hub's Bike Gadget Contest. WOOt! 

Then we set about testing the Speed Vest in real traffic. We've had great success with it, and 
the feedback from everyone who's seen it has been wonderful. Many people want their own. 

Also, simulating a wheel with your hands, and seeing how fast you can make the speed display 
go, has become a strangely compelling party game. 


Download all project code, schematic diagrams, and templates at . 

Keep up with the Speed Vest project at . 

This project first appeared in MAKE Volume 19 , page 100. 

This document was last generated on 201 2-1 1 -01 06:01 :56 PM. 

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